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Assessment of cyclic deformation and critical stress amplitude of jointed rocks via cyclic triaxial testing

Journal of Rock Mechanics and Geotechnical Engineering 2023年第6期15卷 1370-1390页

作者： Waranga Habaraduwa Peellage behzad fatahi Haleh Rasekh School of Civil and Environmental Engineering University of Technology SydneySydneyAustralia

Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress *** samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 *** each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was *** of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(*** dynamic deviatoric stress)beyond which the jointed rock specimens *** measured critical dynamic deviatoric stress was less than the corresponding static deviatoric *** cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic ***,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading *** triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.

关键词： Cyclic triaxial test Jointed rock Joint surface Confining pressure Cyclic deviatoric stress amplitude Failure Residual deformation Dissipated energy

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Effect of constructing twin tunnels under a building supported by pile foundations in the Sydney central business district

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Underground Space 2019年第4期4卷 261-276页

作者： Hadi Khabbaz Robert Gibson behzad fatahi School of Civil and Environmental Engineering University of Technology Sydney(UTS)Australia

In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and *** problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are *** paper focuses on the risks of tunneling beneath Sydney’s Martin Place and how buildings are subject to additional loads caused by *** key objective of this study is to improve the understanding of tunnel-rock-pile interactions and to encourage sustainable development.A finite element model is developed to predict the interaction between tunnel construction and piled *** tunnel,rock,and pile components are studied separately and are then combined into a single *** ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop *** piles are designed using Australian Standards and observations of high-rise *** tunnel construction is modeled based on the construction sequence of a tunnel boring *** combining the components,a parametric study on the relationship between tunnel location,basements,and piles is *** findings,thus far,show that tunneling can increase the axial and flexural loads of piles,where the additional loading exceeds the structural capacity of some piles,especially those that are close to basement *** parametric study reveals a strong relationship between tunnel depth and lining stresses,while the relationship between tunnel depth and induced pile loads is less ***,the horizontal tunnel position relative to piles shows a stronger relationship with pile *** research into tunnel-rock-pile interactions is recommended,especially beneath basements,to substantiate the results of this study.

关键词： Twin tunnels Finite element modeling Pile foundations Plaxis Sydney central business district

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Real-time determination of sandy soil stiffness during vibratory compaction incorporating machine learning method for intelligent compaction

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第5期14卷 1609-1625页

作者： Zhengheng Xu Hadi Khabbaz behzad fatahi Di Wu School of Civil and Environmental Engineering University of Technology SydneySydneyAustralia

An emerging real-time ground compaction and quality control, known as intelligent compaction(IC), has been applied for efficiently optimising the full-area compaction. Although IC technology can provide real-time assessment of uniformity of the compacted area, accurate determination of the soil stiffness required for quality control and design remains challenging. In this paper, a novel and advanced numerical model simulating the interaction of vibratory drum and soil beneath is developed. The model is capable of evaluating the nonlinear behaviour of underlying soil subjected to dynamic loading by capturing the variations of damping with the cyclic shear strains and degradation of soil modulus. The interaction of the drum and the soil is simulated via the finite element method to develop a comprehensive dataset capturing the dynamic responses of the drum and the soil. Indeed, more than a thousand three-dimensional(3D) numerical models covering various soil characteristics, roller weights, vibration amplitudes and frequencies were adopted. The developed dataset is then used to train the inverse solver using an innovative machine learning approach, i.e. the extended support vector regression, to simulate the stiffness of the compacted soil by adopting drum acceleration records. Furthermore, the impacts of the amplitude and frequency of the vibration on the level of underlying soil compaction are *** proposed machine learning approach is promising for real-time extraction of actual soil stiffness during compaction. Results of the study can be employed by practising engineers to interpret roller drum acceleration data to estimate the level of compaction and ground stiffness during compaction.

关键词： Intelligent compaction Machine learning method Finite element modelling Acceleration response

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Influence of particle contact models on soil response of poorly graded sand during cavity expansion in discrete element simulation

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第6期10卷 1154-1170页

作者： Yang Dong behzad fatahi Hadi Khabbaz Henry Zhang School of Civil and Environmental Engineering University of Technology Sydney (UTS) WSP in Australia & New Zealand Sydney Office

The discrete element method(DEM) has been extensively adopted to investigate many complex geotechnical related problems due to its capability to incorporate the discontinuous nature of granular materials. In particular, when simulating large deformations or distortion of soil(e.g. cavity expansion),DEM can be very effective as other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly to the problems concerning in situ testing, pile installation and so forth. In addition, the behaviour of geomaterials in a macro-level is utterly determined by microscopic properties, highlighting the importance of contact models. Despite the fact that there are numerous contact models proposed to mimic the realistic behaviour of granular materials, there are lack of studies on the effects of these contact models on the soil ***, in this study, a series of three-dimensional numerical simulations with different contact constitutive models was conducted to simulate the response of sandy soils during cylindrical cavity expansion. In this numerical investigation, three contact models, i.e. linear contact model, rolling resistance contact model,and Hertz contact model, are considered. It should be noted that the former two models are linear based models, providing linearly elastic and frictional plasticity behaviours, whereas the latter one consists of nonlinear formulation based on an approximation of the theory of Mindlin and Deresiewicz. To examine the effects of these contact models, several cylindrical cavities were created and expanded gradually from an initial radius of 0.055 m to a final radius of 0.1 m. The numerical predictions confirm that the calibrated contact models produced similar results regarding the variations of cavity pressure, radial stress, deviatoric stress, volumetric strain, as well as the soil radial displacement. However, the linear contact model may resu

关键词： Discrete element method(DEM) Cavity expansion Contact models Behaviour of geomaterials

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